Process of making alkali metal chlorites



Patented Oct. 19, 1943 Edward Cornelius Soule, Niagara Falls, N. Y asf signor to The Mathleson Alkali Works, Inc.,- New York, N. Y.', a corporation. Virginia 1 No Drawing. Application June 13, 1941,

Serial n. 397,868 I 2Claims. (01.23-85) My invention relates to the production 01' alkali metal chlorites from chlorine dioxide.,

Chlorine dioxide can be reduced, quantitatively, with peroxides of the alkaline earth metals to form the corresponding alkaline earth metal chlorite. Chlorine dioxide can also be reduced with alkali metal peroxides, but this reaction is less eflicie'nt than that with the alkaline earth metal peroxides. It has also been proposed to reduce chlorine dioxide with hydrogen peroxide in the presence of caustic alkalies with formation of the alkali metalchlorite, butthis reaction is accompanied by losses, prohibitive in the practical sense, of hydrogen peroxide. Refrigeration of the reaction mixture will reduce these losses, but not enough to permit practical application of the reaction. Such attempts to reduce chlorine dioxed with hydrogen peroxide have fallen far short of the eificiency, measured by consumption of hydrogen peroxide, of the theoretical equation as follows:

I have now discovered that this reduction of chlorine dioxide to produce alkali metal chlorites can be carried on with substantially quantitative hydrogen peroxide, 27.43% H202 ibyweight), and '1 suflicien't-water to complete solution ofthe so dium bicarbonate, 2.23 moles of Hi0.- solution is stable at temperatures-of-23-25l 1C.

Chlorine dioxide diluted with air to a safe handling concentration, for example to ,maintaina partial pressure of chlorine dioxide not exceeding Excess chlorine dioxide is then stripped from they consumption of hydrogen peroxide and substan- I tially quantitative conversion to alkali metal chlorite, according to the following type equation, if the alkali metal is supplied to the reaction as alkali metal bicarbonatez.

Thus, the improvement of my invention consists essentially in absorbing chlorine dioxide in an aqueous solution containing hydrogen peroxide and the alkali metal bicarbonate. High chemical efllciency, both with respect to consumption of hydrogen peroxide and with respect to converspecific examples:

Sodium bicarbonate, 0.0503 mole of chemically pure NaI-ICOs, is dissolved in hydrogen peroxide, 0.0251 mole of H202 as commercial 100 volume solution by aeration. The solution should-then"- be free from chlorate, chloride and hydrogen peroxide. In one such operation I recovered 0.0501 mole of sodium chlorite, substantially 100% "of the'theoretical recovery, in the solu-'- tion thusformed.

' a II A slurry is prepared from 0.201 mole of chemically pure NaHCOa, 0.1004 mole of H202 as-the same commercial 100 volume hydrogen peroxide,- and 3.34 moles of H20. Chlorine dioxide diluted with air is introduced into this slurry until chlorine dioxide appears in the eilluent gases while maintaining a temperature of about 24-26 C. Excess chlorine ,dioxide is then stripped from the resulting solution by'aeration. A clear concentrated solution of aqueous sodium chlorite is produced. This solution should be free from chlorate and chloride. In one such operation I recovered 0.1977 mole of sodium chlorite, 98.9% of the theoretical recovery! in the resulting solution.

. III

chlorine dioxide is then stripped from th solu* tion by aeration. Upon standing, crystalline potassium chlorite precipitatesfrom the concentrated solution thus produced without evapora-v tion. The product should be free from chlorate and chloride and the solution should be free from hydrogen peroxid In one such operation I recovered 0.0990 mole'of potas ium chlorite, 99%

otthe theoretica reco ry.

Sodium bicarbonate, 0.0503 mole of chemically pure NaHCOa, is dissolved in hydrogen peroxide, 0.0251 mole of the same commercial 100 volume product, and sufficient water to complete solution, from 0.28 to 0.35 mole of H20. Chlorine dioxide diluted with air is introduced into this solution until chlorine dioxide appears in the eflluent gases while maintaining a temperature of 32-36 C. Excess chlorine dioxide is then stripped from the solution by aeration. In one such operation I recovered 0.0485 mole of sodium chlorite, 97.1% of the theoretical recovery, in the solution thus produceda My invention provides for direct production of concentrated solutions, free from impurities, of the alkali metal chlorites. Thus, solutions from which the chlorit can be separated as a. solid without concentration by evaporation can be produced, or concentrated solutions produced in this manner may be dried, in appropriate apparatus,

for the production of solid chlorite of high purity. Refrigeration is not required to prevent losses of hydrogen peroxide. The reaction can be carried on at temperatures as high as 40 C. or at even higher temperatures. In the higher range of temperatures, it is advantageous to limit the amount of hydrogen peroxide in the reaction mixture at any one time to that justsuflicient to maintain the presence of hydrogen peroxide against the consumption involved. ,The absorption of chlorine dioxid i substantially complete as long as some free hydrogen peroxide is present in the alkali metal bicarbonate solution. The

products of the reaction, other than sodium chlorite and water,are carbon dioxide and oxygen which pass through the reaction mixture with the diluting air without contamination of the solution. I'his carbon dioxide and oxygen may be recovered in the production of alkali metal bicarbonates and hydrogen peroxide in a cyclic manner.

I claim:

1. In the production of alkali metal chlorites, the improvement which comprises absorbing chlorine dioxide in an aqueous solutioncontaining hydrogen peroxide and an alkali metal bicarbonate.

2. In the production of alkali metal chlorites,

the improvement which comprises absorbing chlorine dioxide in an aqueous solution of hydrogen peroxide and an alkali metal bicarbonate wherein the initial molar ratio of hydrogen peroxide to alkali metal bicarbonate is substantially 1:2.

EDWARD CORNELIUS'SOULE. 

